Solve for $n$: $0.03n + 0.08(20 + n) = 12.6$.
Explanation: Expanding the product on the left gives $0.03n + 0.08\cdot 20 + 0.08n = 12.6$.  Simplifying the left side gives $0.11n + 1.6 = 12.6$.  Subtracting 1.6 from both sides gives $0.11n = 11$, and dividing by 0.11 gives $n = \boxed{100}$.